Chlorine gas is a very important chemical product and raw material, and is widely used in many industries such as metallurgical, textile, pharmaceutical, and petrochemical industries. Only one of two chlorine atoms in the chlorine gas molecule can be effectively utilized when the reaction occurs, so the effective utilization rate of chlorine gas is no more than 50%, namely, 1 mole of a by-product hydrogen chloride is generated per 1 mole chlorine gas consumed. Thus, in various industries, the amount of hydrogen chloride generated as by-product is enormous. How to deal with the large amount of hydrogen chloride has become an issue to be urgently solved. Currently, the main measure actually adopted in the industry is to absorb hydrogen chloride with water to prepare low-value, inexpensive hydrochloric acid for sale; since hydrochloric acid is inexpensive and has a limited market demand, the preparation of hydrochloric acid from hydrogen chloride has become a burden rather than a resource. Another measure is to neutralize hydrogen chloride with a base for direct discharge; however, with increasing sophistication of environmental laws and regulations, environmental protection standards of various ways of discharge have become very stringent.
Thus, the methods of preparing chlorine gas from hydrogen chloride that can be industrialized have become a continuing interest in the art. The method of preparing chlorine gas directly from the by-product hydrogen chloride can not only achieve closed circulation of chlorine element, but also achieve zero emissions in the reaction process. Up to now, the methods of preparing chlorine gas from hydrogen chloride can be divided into three main categories: electrolytic method, direct oxidation method, and catalytic oxidation method. The electrolytic process has a high energy consumption and uses an ionic membrane that needs to be frequently replaced, resulting in a very high cost, wherein the cost per ton chlorine gas recovered is greater than 4,000 RMB. The direct oxidation method suffers from a low yield and cannot be industrialized. In contrast to the electrolytic method and the direct oxidation method, the catalytic oxidation method, particularly, the Deacon catalytic oxidation, exhibits the highest potential for industrialization.
The Deacon reaction is one reaction for oxidation of hydrogen chloride into chlorine gas in the presence of a support loaded with a catalyst. The equation of the Deacon reaction is:
            2      ⁢      HCl        +          1      ⁢              /            ⁢      2      ⁢              O        2              ⁢      →    catalyst    ⁢            Cl      2        +                  H        2            ⁢              O        .            The properties of the catalyst have a great influence on the Deacon reaction. Thus, in order to achieve industrialization of the Deacon reaction, domestic and foreign researchers have conducted intensive studies in an attempt to find a suitable catalyst. However, to date, the Deacon method still has disadvantages: for example, the catalyst activity remains to be further improved; in a fixed bed reactor, too high hot-spot temperature in the bed often results in reduced activity and shortened lifetime of the catalyst, and thus, the catalyst needs to be frequently replaced; in a fluidized bed reactor, the catalyst is seriously worn and needs to be continuously supplemented.
The fluidized bed reactors using the Deacon method disclosed in CN87104744 and U.S. Pat. No. 4,994,256 require that the catalysts have sufficient hardness and abrasion resistance and that the walls of the reactors have strong wear resistance. The fixed bed reactors using the Deacon method disclosed in US2004115118, JP2001199710, and U.S. Pat. No. 5,084,264 use heat dissipation devices having a complex structure to reduce the harm of reaction overheating on the catalyst lifetime. A reactor system is disclosed in CN101448734 that can use both a fixed bed and a fluidized bed, but this invention does not disclose the effective lifetime of the catalysts therein.
Given that the catalytic oxidation of hydrogen chloride is exothermic and many catalysts are easily deactivated due to high temperature, it is essential to remove and utilize reaction heat in the Deacon method. The reaction temperature of 600-900° C. on the one hand can result in permanent deactivation of catalysts and on the other hand can result in adverse shifting of the reaction equilibrium toward raw materials at a high temperature, thereby affecting the conversion rate. Accordingly, the advantageous reaction temperature in the Deacon method is 150-600° C.